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Toshiba has produced a fuel cell with no moving parts. Instead of pumps, the tiny 5.6 x 2.2 x 0.5-0.9cm power pack uses a "concentration gradient" to feed fuel and oxygen to the catalyst-covered electrode where they react to generate electricity.

The company claims the unit, unveiled as a prototype yesterday, is the world's smallest 100mW fuel cell.

Like other fuel cells, the Toshiba unit is a direct methanol fuel cell (DMFC). Methanol in a ten per cent concentration touches an electrode separated from a second electrode by a polymer membrane. When air is brought into contact with the second electrode, current flows through any circuit linking the two electrodes.

Getting the membrane right is crucial to preventing air and methanol combining without starting a power-generating reaction. Another problem is the need to pack in enough high-concentration methanol to provide either a long running time or to use as small a fuel reservoir as possible before reducing the concentration sufficiently to trigger the reaction.

Toshiba's prototype uses a structure that progressively dilutes the methanol as it passes from the fuel tank to the reaction chamber. The structure causes methanol to flow through the system without the need to drive it with a pump. The downside is that the cell generates less power, but that makes it more suitable for highly mobile applications.

The refillable fuel tank holds 2cc of methanol in 99.5 per cent concentration - almost ten times the concentration required for the power-producing reaction.

The 8.5g cell generates 100mW of power - enough, Toshiba said, to run am MP3 player for 20 hours.

Last October, the company unveiled a 130g DMFC designed to be used to recharge a phone's own battery rather than as a replacement for it. It generated an average output of 1W and can run for 20 hours - enough, says Toshiba, to recharge a typical phone battery six times.

In March both NEC and Hitachi demonstrated notebook-oriented fuel cells, as did Toshiba. Intel-funded start up PolyFuel is also working on direct methanol fuel cells for laptops. So is German company Smart Fuel Cells.

Toshiba expects to commercialise DMFC technology for PCs in 2004 and for smaller handheld devices in 2005. ®